This invention relates generally to polycrystalline diamond compact (“PDC”) cutters. More particularly, this invention relates to methods to repair worn or eroded PDC cutters, the repaired cutters, and use of the repaired cutters in drill bits and/or other tools.
FIG. 1 shows a perspective view of a drill bit 100 in accordance with the prior art. Referring to FIG. 1, the drill bit 100 includes a bit body 110 that is coupled to a shank 115. The shank 115 includes a threaded connection 116 at one end 120. The threaded connection 116 couples to a drill string (not shown) or some other equipment that is coupled to the drill string. The threaded connection 116 is shown to be positioned on the exterior surface of the one end 120. This positioning assumes that the drill bit 100 is coupled to a corresponding threaded connection located on the interior surface of a drill string (not shown). However, the threaded connection 116 at the one end 120 is alternatively positioned on the interior surface of the one end 120 if the corresponding threaded connection of the drill string (not shown) is positioned on its exterior surface in other exemplary embodiments. A bore (not shown) is formed longitudinally through the shank 115 and the bit body 110 for communicating drilling fluid from within the drill string to a drill bit face 111 via one or more nozzles 114 during drilling operations.
The bit body 110 includes a plurality of blades 130 extending from the drill bit face 111 of the bit body 110 towards the threaded connection 116. The drill bit face 111 is positioned at one end of the bit body 110 furthest away from the shank 115. The plurality of blades 130 form the cutting surface of the drill bit 100, which may be an infiltrated matrix drill bit. One or more of these plurality of blades 130 are either coupled to the bit body 110 or are integrally formed with the bit body 110. A junk slot 122 is formed between each consecutive blade 130, which allows for cuttings and drilling fluid to return to the surface of the wellbore (not shown) once the drilling fluid is discharged from the nozzles 114. A plurality of cutters 140 are coupled to each of the blades 130 within the sockets 180 formed therein, and extend outwardly from the surface of the blades 130 to cut through earth formations when the drill bit 100 is rotated during drilling. One type of cutter 140 used within the drill bit 100 is a PDC cutter; however other types of cutters are contemplated as being used within the drill bit 100. The cutters 140 and portions of the bit body 110 deform the earth formation by scraping and/or shearing. The cutters 140 and portions of the bit body 110 are subjected to extreme forces and stresses during drilling which causes surface of the cutters 140 and the bit body 110 to wear. Eventually, the surfaces of the cutters 140 and the bit body 110 wear to an extent that the drill bit 100 is no longer useful for drilling and is either repaired or discarded depending upon the type of damage and/or the extent of the damage. Although one embodiment of the drill bit has been described, other drill bit embodiments or other downhole tools that use PDC cutters, which are known to people having ordinary skill in the art, are applicable to exemplary embodiments of the present invention.
FIGS. 2A and 2B show various views of a PDC (Polycrystalline Diamond Compact) cutter 140 in accordance with the prior art. FIG. 2A is a perspective view of the PDC cutter 140 in accordance with the prior art. FIG. 2B is a side view of the PDC cutter 140 in accordance with the prior art. These PDC (Polycrystalline Diamond Compact) cutters 140 are commonly used in oil and gas drill bits 100 (FIG. 1), and in other downhole tools. Referring to FIGS. 2A and 2B, the PDC cutters 140 provide a superhard material layer 210, such as a diamond table, which has been fused at high pressure and high temperature (“HPHT”) to a metal backing, or substrate 220, typically tungsten carbide. The PCD cutting table 210, or diamond table, is about one hundred thousandths of an inch (2.5 millimeters) thick; however, the thickness is variable depending upon the application in which the PCD cutting table 210 is to be used. The substrate 220 includes a top surface 222, a bottom surface 224, and a substrate outer wall 226 that extends from the circumference of the top surface 222 to the circumference of the bottom surface 224. The PCD cutting table 210 includes a cutting surface 212, an opposing surface 214, and a PCD cutting table outer wall 216. The PCD cutting table outer wall 216 is substantially perpendicular to the plane of the cutting surface 212 and extends from the outer circumference of the cutting surface 212 to the circumference of the opposing surface 114. The opposing surface 214 of the PCD cutting table 210 is coupled to the top surface 222 of the substrate 220. According to some exemplary embodiments, the cutting surface 212 is formed with at least one bevel (not shown) along the circumference of the cutting surface 212.
Upon coupling the PCD cutting table 210 to the substrate 220, the cutting surface 212 of the PCD cutting table 210 is substantially parallel to the substrate's bottom surface 224. Additionally, the PDC cutter 140 has been illustrated as having a right circular cylindrical shape; however, the PDC cutter 140 is shaped into other geometric or non-geometric shapes in other examples. In certain examples, the opposing surface 214 and the top surface 222 are substantially planar; however, the opposing surface 214 and/or the top surface 222 is non-planar in other examples.
The PDC cutters 140 are expensive to manufacture and constitute a significant portion of the cost of PDC mounted bits 100 (FIG. 1) and tools. PDC cutters 140 are typically brazed into sockets 180 (FIG. 1) formed in the body of a bit 100 (FIG. 1) or tool. This braze joint is frequently the “weak link” in the durability of the tool. A good braze joint requires a very narrow clearance between the socket 180 (FIG. 1) and the PDC cutter 140 that is being brazed into it. A clearance in the range of 0.002 inches or less is desired between the socket 180 (FIG. 1) and the PDC cutter 140 when positioned within the socket 180 (FIG. 1) prior to applying the braze material. A looser fit, i.e. a large clearance, can weaken the braze joint and result in the loss of the PDC cutter 140 in application, thereby shortening the useful life of the bit 100 (FIG. 1) or tool.
FIGS. 3A-3E show several views of damaged PDC cutters 300, 310, 320, 330 in accordance with the prior art. FIG. 3A is a perspective view of a damaged PDC cutter 300 that is heavily worn and eroded in accordance with the prior art. FIG. 3B is a perspective view of a damaged PDC cutter 310 that is slightly eroded in accordance with the prior art. FIG. 3C is a perspective view of a damaged PDC cutter 320 that is heavily eroded in accordance with the prior art. FIG. 3D is a perspective view of a damaged PDC cutter 330 that is eroded in accordance with the prior art. FIG. 3E is a side view of the damaged PDC cutter 330 in accordance with the prior art. Referring to FIGS. 3A-3E, some damaged PDC cutters 310 that have been slightly worn or eroded have historically been rotated to a “full cylinder” section of the tungsten carbide substrate 220 to be reused while orienting a virgin diamond cutting edge towards the formation. If the damaged PDC cutters 300, 320, 330 are too heavily worn or eroded, such as that shown in FIGS. 3A, 3C, 3D, and 3E, the damaged cutters 300, 320, 330 typically are discarded as scrap. In some instances the scrapped cutters 300, 320, 330 have been reclaimed by using wire EDM to cut out a smaller diameter cylinder to make a recovered smaller diameter cutter (not shown). This method does not allow for the direct reuse of the cutter in a similar bit or tool, but instead, the recovered smaller diameter cutter must be deployed in a tool that can economically accommodate the smaller diameter cutter, i.e. has a pocket dimensioned to fit and use the smaller diameter cutter.
The decision as to whether or not a worn or eroded cutter is reused, rotated, or discarded has been based in part on the condition of the remaining tungsten carbide substrate. The criterion depends on the amount of full cylinder substrate remaining. If an insufficient amount of full cylinder substrate remains to allow for a strong braze joint when oriented with a fresh diamond edge towards the formation, then the cutter is typically scrapped or reprocessed as described above.
The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments.